Device for controlling the brightness of an instrumentation light of an automobile

ABSTRACT

A device for controlling the brightness of dashboard lights in a motor vehicle is described, where an optoelectric receiver adjusts the light intensity of the dashboard lights with the output signal as a function of ambient brightness. To obtain an automatic measurement of the ambient brightness distribution in the direction of vehicle travel, taking into account the brightness in certain regions in the vicinity of the vehicle, an image sensor pointing in the direction of vehicle travel is provided as an optoelectric receiver to perform a location-selective absolute brightness measurement, and its electric output signal, weighted with preselected or preselectable algorithms for determining ambient brightness by an analyzer unit, so it can be sent to a control unit to influence the brightness of the dashboard lights.

BACKGROUND INFORMATION

The present invention relates to a device for controlling the brightnessof dashboard lights in a motor vehicle, in which an electro-opticaltransducer aligned in the direction of travel changes the lightintensity of the dashboard lights, using the output signal, as afinction of the ambient brightness in front of the vehicle, and theoutput signal of the electro-optical transducer, which is weighted by anevaluation unit using predefined algorithms, being supplied to a controlunit for influencing the brightness of the dashboard lights.

A device for controlling the brightness of dashboard lights is describedin German Published Patent Application No. 32 45 299. In this case, aphotodetector is used as an electro-optical transducer, which is joinedto the windshield of the motor vehicle by a fiber-optic guide. In thismanner, the photodetector detects the brightness of the ambient range infront of the motor vehicle. The output signal of the photodetector,which is weighted by a microprocessor using predefined algorithms, issupplied to a control unit for changing the brightness of the dashboardlights. The brightness of the ambient range in front of the motorvehicle is only approximately monitored by this device, meaning that thechange in brightness of the dashboard lights is inadequate, especiallywhen there are objects driving ahead or objects located in the ambientrange.

A similar device having a phototransistor as an electro-opticaltransducer is described in German Published Patent Application No. 44 09777. The analog output signal of the phototransistor is converted into adigital signal, and the characteristic curve of the phototransistor iscompensated for by a processing device in such a manner, that a signalproportional to the ambient brightness is acquired for changing thebrightness of the dashboard lights.

Japanese Laid-Open Patent No. 60 24 0545 describes a device forautomatically switching the headlights of a vehicle on and off, when itdrives into and out of a tunnel. In this case, the change in thebrightness in front of the vehicle is monitored using animage-processing sensor, e.g. a CCD camera, and the change is used by anevaluation and control unit for switching the headlights.

A CCD camera for controlling the brightness of the dashboard lights isnot suitable as an electro-optical transducer, since the CCD camera hasa small dynamic range and does not allow an absolute determination ofbrightness. An absolute determination of brightness would only beattainable by aperture and illumination-time regulation, which, however,can never be exactly determined.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a device in which theabsolute ambient brightness in front of the motor vehicle is detectedand used for optimally adjusting the brightness of the dashboard lights.

This object is achieved by the present invention, in that a logarithmicCMOS image-processing sensor used as an electro-optical sensor andhaving a non-linear conversion characteristic, decreases with increasingincident light.

An extreme dynamic range is achieved by this new image-processing sensorhaving a non-linear conversion characteristic, which will allow a largebrightness range to be imaged in a technically limited voltage orcurrent range.

In this context, the output signal of the image-processing sensor canalso be weighted using suitable object-detection algorithms. Forexample, this can prevent a truck painted in a dark color from causingthe ambient-brightness signal to be too small. Additional sensors (LidarRadar) can also acquire information about an object, which is suppliedto the evaluating unit and used in the above-described manner forcontrolling the brightness of the dashboard lights.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a section along the longitudinal axis of the motor vehiclewith the positioning of the image sensor.

FIG. 2 shows the nonlinear conversion characteristic of the imagesensor.

FIG. 3 shows a block diagram of the device for controlling thebrightness of the dashboard lights

An image sensor 2 (camera) is arranged in the interior of a motorvehicle 1 in the upper area behind the windshield. The space behind therearview mirror (not shown) which is mounted in this area is preferablyused for this purpose. Image sensor 2 points in the direction of vehicletravel and detects the conical traffic zone in front of motor vehicle 1as indicated. Image sensor 2 is composed of multiple individual sensorsfor measuring the absolute brightness of the detected traffic zone in alocation-selective manner.

As FIG. 2 shows, image sensor 2 has a nonlinear conversioncharacteristic. With an increase in light signal L, there is also anincrease in voltage U or current I delivered, but slope ΔU/ΔL or ΔI/ΔLdecreases. This leads to implementation of a highly dynamic image sensor2. With a technically limited voltage or current range, a largebrightness range can be imaged. It is especially advantageous to use animage sensor with a logarithmic conversion characteristic, because thenthe contrast resolution is constant over a brightness range of multipledecades.

Image sensor 2 supplies an electric “surface” image signal to ananalyzer unit 3 which analyzes the image signal with the goal ofmeasuring the ambient brightness. The ambient brightness signal or adashboard brightness signal derived from it is relayed over a bus line 8to a control unit 4 which controls dashboard lights 5. Analyzer unit 3can weight the image signal of image sensor 2 according to preselectedalgorithms of object detection and use it for a suitably adjustedcontrol of dashboard lights 5. Additional sensors 6 optionally providedfor object detection or for other functions send additional informationfor adjusting the control signals for control unit 4 of dashboard lights5 over a bus line 8 of analyzer unit 3. Sensors 6 may be used for objectdetection and for detection of the condition of the vehicle lighting.

What is claimed is:
 1. A device for controlling a brightness of a dashboard light in a motor vehicle, comprising: an electro-optical transducer aligned in a direction of travel and for producing an output signal that changes a light intensity of the dashboard light as a function of an ambient brightness in front of the motor vehicle, wherein: the electro-optical transducer includes a logarithmic CMOS image-processing sensor having a non-linear conversion characteristic, and the CMOS image-processing sensor produces a decrease in the output signal of the electro-optical transducer as an increase occurs in an incident light signal; an evaluation unit for weighting the output signal of the electro-optical transducer in accordance with predefined algorithms; and a control unit supplied with the output signal of the electro-optical transducer for influencing the brightness of the dashboard light.
 2. The device according to claim 1, further comprising: a plurality of additional sensors for providing further information to the evaluation unit.
 3. The device according to claim 1, wherein: the CMOS image-processing sensor is positioned between a windshield of the motor vehicle and a rearview mirror mounted at a top of the windshield at a location approximately in a middle of the windshield. 